Retinas of normal rhesus monkeys and albino rats were exposed to lights of various natures and densities. The exposed retinas were excised at various time intervals and studied by electron microscopy. Retinas exposed to electronic flash for a short period of time showed multiple breakage of the plasma membrane of the outer segment prior to the occurrence of damage in the photoreceptor disc membrane. Groups and individual disc membranes spill out through the broken cell membrane into the subretinal space. These disc membranes are then phagocytized by the pigment epithelium. This change is considered to be a type of photoreceptor turn-over process. Turn-over of cone outer segments, in which no large phagosomes are formed, may be carried out by a similar process.